The present invention relates to an improved method and apparatus for full duplex communication over a communication channel; specifically to an improved method for achieving ping-pong communications over an optical fiber.
Modern telephone systems require that a calling and a called station be able to communicate simultaneously. To achieve this objective, full duplex communication is used wherein each station can transmit/receive concurrently. Full duplex communication can be achieved with separate transmit/receive channels or over a single channel by properly timing data transmission and data reception at each station (allowing for apparent simultaneous transmission and reception). Existing ping-pong communication schemes which allow apparent full duplex communication over a single channel require more complex and more costly circuitry than that of the present invention.
For instance, Hastings U.S. Pat. No. 5,075,791 discloses a method of apparent full duplex communication which involves the compression and transmission of data in bursts through an optical fiber. A transmitting station becomes receptive to incoming bursts of data sent from a distant station only after a fixed delay period following the transmission of data. To achieve this result, Hastings requires relatively complex and expensive timing and data compression circuitry. Also, Hastings does not appear to compensate for a change in propagation delay that occurs as the optical fiber's length changes.
LaGess U.S. Pat. No. 5,046,063 discloses a ping-pong communication system and method wherein one station is designated a master and another station is designated a slave. The master station transmits data bursts at fixed time intervals while the slave station transmits data burst only upon the receipt of data from the master station. Either the master station transmission rate or the slave's response time may be varied to ensure that data transmission does not occur during the time period that data should be received.
Kanaji U.S. Pat. No. 4,720,827 employs a master/slave scheme similar to that of LaGess with the additional inclusion of Sync supervision and time setting information within the data bursts. Master/slave systems are undesirable because they introduce complexity and expense to a communications system. For instance, because each station must be able to function as both a master and a slave, both master and slave control circuitry must be included in each station.
Accordingly, it is an object of the present invention to provide an apparatus and method which permits apparent full duplex communication over a communication channel with much simpler and less expensive circuitry than that required of master/slave or data compression architectures. It is a further object of the invention to provide an apparatus and method which compensates for variations in channel propagation delay.